The Journal of Neuroscience, June 1, 2002, 22(11):4468-4477
Bcl-2 Overexpression Does Not Enhance
In Vivo Axonal Regeneration of Retinal Ganglion Cells
after Peripheral Nerve Transplantation in Adult Mice
Tetsu
Inoue1,
Mizuho
Hosokawa1, 2,
Katsuko
Morigiwa1,
Yuichi
Ohashi2, and
Yutaka
Fukuda1
1 Department of Physiology and Biosignaling, Graduate
School of Medicine, Osaka University, Osaka 565-0871, Japan, and
2 Department of Ophthalmology, School of Medicine, Ehime
University, Ehime 791-0295, Japan
Optic nerve (ON) injury in adult mammals causes retinal ganglion
cell (RGC) death and subsequent visual loss. Recovery of vision
requires both rescuing axotomized RGCs and inducing their axonal
regeneration. Axotomized RGCs are significantly rescued by
overexpression of bcl-2, an anti-apoptotic gene.
However, whether bcl-2 affects axonal regeneration is
controversial. In neonatal bcl-2 transgenic mice
(bcl-2 mice), optic tract regeneration after tectal
lesion was promoted (Chen et al., 1997), whereas ON regeneration after
ON crush was not (Lodovichi et al., 2001). These conflicting results
may be attributable to different environments between tectum and ON. We
tested here whether bcl-2 overexpression enhances in vivo RGC axonal regeneration in adult mice through a
permissive environment in the peripheral nerve (PN) graft. Four weeks
after PN transplantation to the proximal ON stump, we assessed the
number of surviving and regenerating RGCs by retrograde labeling.
Although the survival rate in bcl-2 mice was
significantly enhanced compared with that in wild-type (wt) mice, the
regeneration rate was not enhanced. In both bcl-2 and wt
mice, RT97 immunostaining of the PN-grafted retinas revealed some RGC
axons regrowing intraretinally but repulsed at the optic disk. To
circumvent this repulsive barrier, we directly transplanted the PN
graft to the partially injured retina and compared regeneration rates
between these mice. Here again the regeneration rate in
bcl-2 mice did not exceed that in wt mice. These
findings indicate that bcl-2 overexpression enhances
survival but not axonal regeneration of adult RGCs even within a
permissive environment.
Key words:
axonal regeneration; survival; retinal ganglion cells; peripheral nerve transplantation; optic nerve; bcl-2
transgenic mice
Copyright © 2002 Society for Neuroscience 0270-6474/02/22114468-10$05.00/0